• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.843-850
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• 2020

The purpose of this study is to evaluate the structural risk and weakness of a railway tank car through nonlinear collision analysis according to overseas collision safety standards. The goal is to propose a crash safety design guideline for railway tank cars for transporting dangerous goods in Korea. We analyzed the buffer impact test procedure of railway freight cars prescribed in EN 12663-2 and the tank puncture test criteria prescribed in 49CFR179. A nonlinear finite element model according to each standard was modeled using LS-DYNA, a commercial finite element analysis solver. As a result of the buffing impact test simulation, it was predicted that plastic deformation would not occur at a collision speed of 6 km/h or less. However, plastic deformation was detected at the rear of the center sill and at the tank center supporting the structure at a collision speed of 8 km/h or more. As a result of a head-on test simulation of tank puncture, the outer tank shell was destroyed at the corner of the tank head when 4% of the kinetic energy of the impacter was absorbed. The tank shell was destroyed in the area of contact with the impacter in the test mode analysis of tank shell puncture when the kinetic energy of the moving vehicle was reduced by 30%. Therefore, the simulation results of the puncture test show that fracture at the tank shell and leakage of the internal material is expected. Consequently, protection and structural design reinforcement are required on railway tank cars in Korea.

• Journal of Korean Society of Steel Construction
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• v.29 no.2
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• pp.181-192
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• 2017

A beam splice method using inclined end-plates and high-strength tension bolts was developed. The end-plates welded to a bracket and a spliced beam are connected each other by using the tension bolts. In the present study, six exterior beam-to-column moment connections were tested under cyclic loading. Test parameters were the end-plate details and bolt arrangements. All specimens were designed so that moment resistances of the end-plates and bolts were greater than the required moment at the beam splice, in accordance with the design methods of AISC Design Guide 4. Test results showed that in the beam splices with the extended end-plates, the beam moment successfully transferred to the bracket, without any defeats such as excessive prying action of the end plates and brittle failure at the end plate-to-beam flange weld joints. However, the deformation capacities of the overall beam-to-column connections were limited due to the brittle failure of the beam-to-column flange weld joints. From the test results, recommendations for seismic design and detailing of the beam-to-column moment connection with inclined end-plate beam splice were given.

• Archives of design research
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• v.15 no.4
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• pp.263-274
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• 2002

This study aims to analyze the image of long-span structures. For the intention, it analyzes the relationship between images and physical attributions of elements such as materials, stresses, configurations, compositions and shapes of structures. The image of structures can represent following 5 factors; friendly-unfriendly, strong-weak, dynamic-calm, superior-inferior, and regular-irregular. The friendly-unfriendly in the image of structure mostly determines on a finished material and partly with a structural shape. The strong-weak in the image of structure determines on configuration of the structural members. The dynamic-calm in the image of structure determines on the structural shape. Hence the structure has dynamic forms when it seems to be open and sharp, namely when it receives the flow of forces in the structural shape, and it has a (-) gauss curved rate or an diagonal appearance. The superior-inferior in the image of structure determines on composition of structural elements. The structure seems to be superior is contributed not simply to support load but positively to create design as a tectonic element. From now on, this study can provide the useful information on the long-span structure design through the more appropriate analysis of the image.

• International Journal of Highway Engineering
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• v.9 no.2 s.32
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• pp.101-114
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• 2007

Dowel bars in the jointed concrete pavement are used to both provide load transfer across pavements joints and prevent the joint faulting leading to longer service life. On the contrary, the misplacement of dowel bar can provide negative results including the joint freezing(locking) that may cause the joint spatting and unexpected mid-slab cracking. The dowel bar can be placed using the assembly or dowel bar inserter (DBI) during the concrete pavement construction. In the domestic practice of the concrete pavement construction, the dowel bar is placed using the assembly method. This study primarily focuses on the comparison of these two dowel placement methods using the field data from the KHC test road in which both dowel placement methods have been applied to a certain length of the concrete pavement. The field data regarding the alignment of the dowel bars placed by both methods was collected using MIT-SCAN2, a nondestructive measuring equipment, and processed to compute Joint Score and Running Ave. Joint Score which are used as indicators of the dowel bar performance. The comparison of the methods for the dowel bar placement using these indicators shows that the DBI method provided much better alignment of the dowel bars reducing the risk of joint freezing than the assembly method. In order to improve the quality of the dowel bar placement using the assembly method, the current weak points of the assembly method including the fabrication, storage, and installation of dowel bar assembly were investigated and the solution was suggested. The improved dowel bar sets based on the suggested solution have been applied to an actual practice of the concrete pavement construction. The field data shows that the improved assembly method suggested in this study can highly reduce the risk of joint freezing.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.4
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• pp.397-411
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• 2004

Purpose: The purpose of this study was to determine the effect of anchorage systems and palatal coverage of denture base on load transfer in maxillary implant-supported overdenture. Material and methods: Maxillary implant -supported overdentures in which 4 implants were placed in the anterior region of edentulous maxilla were fabricated, and stress distribution patterns in implant supporting bone in the case of unilateral vertical loading on maxillary right first molar were compared with each other depending on various types of anchorage system and palatal coverage extent of denture base using three-dimensional photoelastic stress analysis. Two photoelastic overdenture models were fabricated in each anchorage system to compare with the palatal coverage extent of denture base, as a result we got eight models : Hader bar using clips(type 1), cantilevered Hader bar using clips(type 2), Hader bar using clip and ERA attachments(type 3), cantilevered milled-bar using swivel-latchs and frictional pins(type 4). Result: 1. In all experimental models, the highest stress was concentrated on the most distal implant supporting bone on loaded side. 2. In every experimental models with or without palatal coverage of denture base, maximum fringe orders on the distal ipsilateral implant supporting bone in an ascending order is as follows; type 3, type 1, type 4, and type 2. 3. Each implants showed compressive stresses in all experimental models with palatal coverage of denture base, but in the case of those without palatal coverage of denture base, tensile stresses were observed in the distal contralateral implant supporting bone. 4. In all anchorage system without palatal coverage of denture base, higher stresses were concentrated on the most distal implant supporting bone on loaded side. 5. The type of anchorage system affected in load transfer more than palatal coverage extent of the denture base. Conclusion: To the results mentioned above, in the case of patients with unfavorable biomechanical conditions such as not sufficient number of supporting implants, short length of the implant, and poor bone quality, selecting a resilient type attachment or minimizing the distal cantilevered bar is considered to be an appropriate method to prevent overloading on implants by reducing cantilever effect and gaining more support from the distal residual ridge.

• 한국지구물리탐사학회:학술대회논문집
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• 2004.08a
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• pp.138-156
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• 2004

GPR(Ground Penetrating Radar) was used for imaging the interior of the historical masonry such as stone pagoda in order to provide the basic information of safely inspection. The scope of the imaging was restricted to the foundation part of stone pagoda that transferred the load of the pagoda to the ground. Kirchhoff migration and traveltime tomography was used for imaging the outer stone and the inside of stone pagoda, respectively. From the migrated images, we could measure the thickness and the shape of the boundaries of the outer stone in the foundation part. From the reconstructed tomograms for the physical model, we could get the GPR propagation velocity distribution and exactly find the position of the air in the model and calculate the average velocity with respect to the different filling materials. The properties and the shape of the interior materials of stone pagoda can be basic informations for the safety inspection.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.411-422
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• 2010

Self-sensing on micro-failure, dispersion degree and relating properties, of carbon nanotube(CNT)/epoxy composites, were investigated using wettability, electro-micromechanical technique with acoustic emission(AE). Specimens were prepared from neat epoxy as well as composites with untreated and acid-treated CNT. Degree of dispersion was evaluated comparatively by measuring volumetric electrical resistivity and its standard deviation. Apparent modulus containing the stress transfer was higher for acid-treated CNT composite than for the untreated case. Applied cyclic loading responded well for a single carbon fiber/CNT-epoxy composite by the change in contact resistivity. The interfacial shear strength between a single carbon fiber and CNT-epoxy, determined in a fiber pullout test, was lower than that between a single carbon fiber and neat epoxy. Regarding on micro-damage sensing using electrical resistivity measurement with AE, the stepwise increment in electrical resistivity was observed for a single carbon fiber/CNT -epoxy composite. On the other hand, electrical resistivity increased infinitely right after the first carbon fiber breaks for a single carbon fiber/neat epoxy composite. The occurrence of AE events of added CNT composites was much higher than the neat epoxy case, due to micro failure at the interfaces by added CNTs.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.5
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• pp.1025-1037
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• 2015

Flexible base isolation bearings that separate superstructure from ground have been widely used in the construction field because they make a significant contribution to increasing the fundamental period of the structure, thereby decreasing response acceleration transmitted into the superstructure. However, the established bearing devices installed to uphold the whole building give rise to some problems involved with failure and collapse due to lack of the capacity as modern structures are getting more massive and higher. Therefore, this study suggests new isolation bearings assembled with additional restrainers enabled to reinforcing and recentering, and then evaluates their performance to withstand the seismic load. The superelastic shape memory alloy (SMA) bars are installed into the conventional lead-rubber bearing (LRB) devices in order to provide recentering forces. These new systems are modeled as component spring models for the purpose of conducting nonlinear dynamic analyses with near fault ground motion data. The LRB devices with steel bars are also designed and analyzed to compare their responses with those of new systems. After numerical analyses, ultimate strength, maximum displacement, permanent deformation, and recentering ratio are compared to each model with an aim to investigate which base isolation models are superior. It can be shown that LRB models with superelastic SMA bars are superior to other models compared to each other in terms of seismic resistance and recentering effect.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.6
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• pp.999-1010
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• 2016

High-strength strands have been increasingly applied to recent actual structures in Korea. Structural effect of the increased spacing of sheaths was investigated in this study when the usual 1,860 MPa strands of an LNG storage tank are replaced with 2,400 MPa high-strength strands. First, finite element models of a cylindrical wall of an LNG tank were established and prestressing effect of the circumferential and vertical tendons was considered as equivalent loads. As a result of varying the tendon spacing and prestressing force with the total prestressing effect kept the same, the stress distribution required in design was obtained with the high-strength strands. Also, a full-scale specimen that corresponds to a part of an LNG tank wall was fabricated with 31 high-strength strands with 15.2 mm diameter inserted in each of two sheaths. It was observed that such a high level of prestressing force can be properly transferred to concrete. Moreover, an LNG tank with the world's largest 270,000 kl capacity was modeled and the prestressing effect of high-strength strands was compared with that of normal strands. The watertightness specifications such as residual compressive stress and residual compression zone were also ensured in case of leakage accident. The results of this study can be effectively used when the 2,400 MPa high-strength strands are applied to actual LNG tanks.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.6
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• pp.1161-1167
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• 2016

In this study, an attempt was made to conduct a case study on the development of ground expansive displacement due to lack of bearing capacity of original ground in spite of applying reinforcement treatments that intended to enhance the stability of big size high-speed rail tunnel in large fault zone. For the purpose of this, in-situ measurements made in the middle of excavation stage were analyzed in order to characterize ground responses and numerical analysis was performed to evaluate the effectiveness of reinforcement technique such as elephant foot method applied for this site via comparing with field monitoring measurements. In addition, further numerical studies were carried out to investigate the influence of leg pile installation angle and length, which is one of types of elephant foot method. The results revealed that the optimum condition for the leg pile installation is to maintain 45 degree of installation angle along with 6 meter of embedment depth.